Method and apparatus for controlling a gas discharge display device

ABSTRACT

Apparatus and method are disclosed for controlling a gas discharge display device which has sealed therein an ionizable gas and electrodes insulated by the gas and low-melting-point glass and in which an alternating sustain voltage is impressed to the electrodes and writing and erasing are achieved by a voltage pen impressed with an AC control voltage and in which the magnitude and/or frequency of the sustain voltage is altered, thereby to ensure writing and erasing.

United States Patent 1191 Nakayama et a1.

[451 Oct. 1, 1974 METHOD AND APPARATUS FOR 4/1971 Mayer et a1 1. 340/166 EL x CONTROLLING A GAS DISCHARGE 3,651,509 3/1972 Ngo 315/169 TV X 3,689,912 9/1972 Dick 340/166 EL X DISPLAY DEVICE 3,727,102 4/1973 Johnson 315/169 TV X [75] inventors: Norihiko Nakayama; Yasunari Shirouchi; Toshinori Urade; Shizuo Andoh, all of Kobe, Japan Primary Examiner-Alfred L. Brody [73] Assignee: Fujitsu, Limited, Kawasaki, Japan Attorney Agent or Flrm staas Halsey & cable [22] Filed: Sept. 18, 1972 [21] App]. N0.: 289,600 [57] ABSTRACT Foreign Application Priority Dam Apparatus and method are disclosed for controlling a Sept. 18, 1971 Japan 46-72861 gas discharge display device which has sealed therein an ionizable gas and electrodes insulated by the gas [52] US. Cl 315/169 TV, 340/166 EL and low-melting-point glass and in which an altemat- [51] Int. Cl. HOSb 41/30 ing sustain voltage is impressed to the electrodes and [58] Field of Search 315/169 TV, 169 R; writing and erasing are achieved by a voltage pen im- 340/324 R, 166 EL, 337 pressed with an AC control voltage and in which the magnitude and/or frequency of the sustain voltage is [56] References Cited altered, thereby to ensure writing and erasing.

UNITED STATES PATENTS 3,559,307 2/1971 Barrekette et a1. 340/337 X 21 Claims, 14 Drawing Figures '3 --l --q l s b 15 i i 1 I2 I l 1151111 CONVERTER CONTROL GENERATOR CIRCUIT E Q 1 VOLTAGE CIRCUIT I DISCHARGE SOURCE lSPLAY EVICE -ll ADDRESS J6 CIRCUIT ADDRESS {l7 POWER SOURCE '8 1 L KEYBOARD KEYBOARD ADDRESS CIRCUIT d" 16 (TO I75) SHIT 1 U 5 ADDRESS KIT POWER SOURCE TIMING GENERATOR CIRCUIT FIG.1

PATENTED H974 SUSTAIN VOLTAGE A GENERATOR CIRCUIT COUNTER PATENTEU 97 SEE! S I 5 FIG. I08

DIVIDER Vs min 21 FROM H7 05 FIG. I?

METHOD AND APPARATUS FOR CONTROLLING A GAS DISCHARGE DISPLAY DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus and method for controlling a gas discharge display device of the type that writing and erasing are carried out by means of a voltage pen.

2. Description of the Prior Art As known under the name of a plasma display panel, in a gas discharge display device, Neon or like discharge gas is sealed between opposed X- and Y- direction electrodes covered with dielectric layers. The electrodes are supplied with a sustain voltage of about 50 KHz, and when a superimposed or single write-in pulse voltage is impressed to selected ones of the electrodes in such a manner that the peak value of the voltage at the selected electrodes may exceed a discharge voltage, a discharge spot is produced at the intersection of the selected electrodes and a wall charge is stored in the dielectric layers to provide a wall voltage. The potential difference between the wall voltage and the sustain voltage applied after a half cycle exceeds the dis charge voltage to produce the discharge spot again and reverse the polarity of the wall voltage. Accordingly, after once produced, the discharge spot is continuously generated by continuous impression of the sustain voltage lower than the discharge voltage, thus enabling a memory display. lmpressing an erasing pulse voltage of small pulse width or lower amplitude than a minimum sustain voltage, the discharge spot is once produced but no wall voltage is thereby generated and no discharge spot is produced by the subsequent sustain voltage. Namely, the display can be erased.

Such a gas discharge display of the type that writing and erasing are achieved by an address method based on selection of the X- and Y-direction electrodes can also be used as a display device for electronic computers. However, it is demanded that an address method such as one employing a light pen and a cathode tube display device be used for the display device thereof.

The address method using the light pen that has heretofore been proposed is such that a light spot is directed by the light pen to an address position in the gas discharge display device suppliedwith the sustain voltage to supply photoelectrons in the discharge cell, thereby achieving writing or erasing. However, this method is difficult to address at a minute point and not easy to obtain accurate operation, and hence regarded as difficult to put to practical use.

Further, an external address method employing a voltage pen has also been proposed. This method is to supply the voltage pen with a voltage of the same frequency as the sustain voltage and reverse its phase 180 thereby to control writing and erasing, for example, as explained in the 1970 IDEA Symposium Digest of Papers, pages 28 and 29. However, such a method is also inaccurate in its erasing operation, and hence is not suitable for use in those fields which require accurate writing or erasing operation.-

SUMMARY OF THE INVENTION This invention is directed to a method of controlling a gas discharge display device and has for its principal object to provide novel apparatus and method for controlling a gas discharge display device which is free from the aforementioned defects experienced in the prior art and ensures achievement of accurate writing and erasing operations by the use of a voltage pen.

Another object of this invention is to provide apparatus and method which ensures achievement of writing and erasing operations of a gas discharge display device by the use of a voltage pen which is simple in construction and easy of operation.

Briefly stated, the apparatus and method of controlling the gas discharge display device according to this invention is such that a sustain voltage source is pro vided with means for changing the magnitude or freqency of the sustain voltage. At the time of writing, addressing is achieved by the voltage pen with the sustain voltage or its frequency being raised; and at the time of erasing, addressing is achieved by the voltage pen with its sustain voltage or frequency being lowered. At the time of writing, superimposition of the voltage impressed by the voltage pen on the sustain voltage ensures achievement of writing operation and, at the time of erasing, since the sustain voltage or its frequency is low, even if the discharge spot is produced by the superimposition of the voltage impressed by the voltage pen on the sustain voltage, the wall voltage is thereby cancelled, thus ensuring erasing operation.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one example of this invention;

FIG. 2 is a cross-sectional view of the principal part of the gas discharge display device shown in FIG. 1;

FIG. 3 is a circuit diagram illustrating one example of the sustain voltage generator circuit shown in FIG. 1;

FIG. 4 is a series of waveform diagrams, for explaining the operation of the circuit depicted in FIG. 3;

FIG. 5 is a circuit diagram showing one example of an address source circuit;

FIG. 6 and 7 are circuit diagrams illustrating examples of an address circuit respectively;

FIG. 8 is a waveform diagram of a sustain voltage;

FIG. 9 is a diagram, for explaining the write-in operation by a voltage pen;

FIGS. 10A and 10B are circuit diagrams showing ex amples of a converter circuit;

FIG. 11 is a diagram, for explaining the erasing operation by the voltage pen;

FIG. 12 is a diagram, for explaining the relationship between a wall voltage and the sustain voltage; and

FIG. 13 is a diagram, for explaining the erasing operation in the case where the frequency of the sustain voltage is lowered.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows in block form one example of this invention. In the figure, reference numeral 10 indicates a gas discharge display device having X- and Y- direction electrodes; 11 a sustain voltage generator circuit; 12 a frequency or voltage converter circuit; 13 a control voltage source; 14 a voltage pen for addressing use; 15 and 16 address circuits; 17 an address power source and 18 a key board and reference character S 3 designates a changeover switch disposable from a first position a to a second posiion b.

FIG. 2 illustrates in section the principal part of the gas discharge display device 10, In the gas discharge display device 10, X- and Y-direction electrodes 3 and 4 are mounted on the interior surfaces of opposed glass base plates 1 and 2 in such a manner as to be perpendicular to each other. The electrodes 3 and 4 are covered with dielectric layers 5 and 6 of low-melting-point glass, and a mixed discharge gas, composed of for example Ne 95 percent and N 5 percent, is sealed within the space 7 defined between the opposing dielectric layers 5 and 6.

FIG. 3 schematically shows the internal construction of one example of the sustain voltage generator circuit 1 1 (FIG. 1). A clock pulse from a clock pulse generator 111 is counted by a scale-of-twelve counter 112. The count contents 1 and 7 of the counter 112 are applied by a sustain voltage timing generator circuit 113 to the bases of transistors Q1 and 02.

FIG. 4 shows a series of waveform diagrams, for explaining the operation of the sustain voltage generator circuit, in which a shows a clock pulse; b to f the count contents of the counter 112, g the output of the transistor Q1, that is a voltage at a terminal 114; h the output of the transistor Q2, that is a voltage at a terminal 115; and i a write-in timing pulse which is obtained by applying the count content of the counter 112 to the address power source 17 from a terminal 116 and to corresponding terminal 175 as will be seen in FIG. 5. Further, terminals 117 and 118 are connected to the converter circuit 12.

FIG. 5 illustrates the internal construction of one example of the address power source 17, in which the terminal 116 in FIG. 3 is connected to a terminal 175. A write-in timing pulse generator circuit 171 produces the timing pulse shown in FIG. 4i, which is applied to AND circuits 173 and 174. Further, a terminal 180 is connected to the key board 18, the output of which is fed to the AND circuits 173 and 174 and decoded by a decoder 172. Terminals 176 and 177 are connected to the address circuits and 16 respectively, while terminals 178 and 179 are also connected to the address circuits 15 and 16 respectively. These terminals 178 and 179 transmit the decoded contents Xl to Xn and Y! to Ym and, in practice, each of them comprises a plurality of terminals.

FIG. 6 shows the internal construction of one example of the address circuit 15, in which terminals 151, 152 and 153 are connected respectively to the terminal 176 of the address power source 17, the changeover switch S and the terminal 178 of the address power source 17. Terminals XLl to XLn are connected to the X-direction electrodes of the gas discharge display device 10 and the sustain voltage divided from the sustain voltage generator circuit 11 is supplied through the changeover switch S to the terminal 152, from which it is impressed to the electrodes through diodes DX2I to DX2n. By the write-in timing pulse, a transistor O3 is turned on to open AND circuits AXl to AXn in response to the decoded contents, so that a voltage Vs is impressed through diodes DXll to DXln to a selected one of the X-direction electrodes of the gas discharge display device 10.

FIG. 7 shows the internal construction of one example of the address circuit 16, in which terminals 161, 162 and 163 are connected to the terminal 177 of the address power source 17, the changeover switch S and the terminal 179 of the address power source 17. Terminals YLl to YLm are connected to the Y-direction electrodes of the gas discharge display device 10. A transistor Q4, diodes DYll to DY1m and DYZI to DY2m and AND circuits AYl to AYm are similar to those in the address circuit 15 described above but since the write-in voltage is -(V V the transistor Q4 and the diodes DYll to DY1m are opposite in conducting direction to those above mentioned.

With such an arrangement as described in the foregoing, the changeover switch S is held in position a and the sustain voltage derived from the sustain voltage generator circuit 11 is impressed to the X- and Y- direction electrodes of the gas discharge display device 10 through the address circuits 15 and 16 respectively. Namely, the sustain voltage is impressed upon the electrodes through the diodes DX2l to DX2n (FIG. 6) and DYZl to DY2n (FIG. 7) at such timing as depicted in FIGS. 43 and 4h and a pulse voltage which becomes alternately positive and negative is applied between the opposing electrodes.

When a signal representative of a letter, a symbol or the like is applied to the address power source 17 together with a position designating signal, the AND circuits 173 and 174 (see FIG. 5) are opened at such timing as shown in FIG. 41' and the AND circuits AXl to AXn (see FIG. 6) of the address circuits l5 and 16 are opened in response to the decoded contents of the decoder 172, by which the voltages V and -(V V are impressed to selected ones of the X- and Y-direction electrodes and a firing voltage V is impressed to the thus selected cell at the intersection of the selected X- and Y-direction electrodes, thus achieving the writing operation.

In the case of erasing the display, the pulse width of the voltage impressed to the selected cell is decreased, for example, by reducing the pulse widths of the timing pulses appearing at the terminal 176 and 177 of the address power source 17 based on an instruction from the key board 18. In such a case, discharge is once achieved but no wall voltage is produced and no discharge is caused even by the subsequent impression of the sustain voltage, thus erasing the display.

Next, a description will be given of the writing operation by the voltage pen 14 in accordance with this invention. Assume that a sustain voltage which has a pulse width of SuS, a repetitive frequency of SOKHZ and a voltage value of V is impressed from the sustain voltage generator circuit 11 to the X- and Y- direction electrodes of the gas discharge display device 10. FIG. 8 shows one example of the waveform of this sustain voltage, in which reference character V indicates a discharge voltage, V the sustain voltage, V a minimum sustain voltage and V a wall voltage of the cell in which a discharge spot is being produced. The condition in which such a sustain voltage is impressed will hereinafter be referred to as a first condition having a large memory factor (which is a factor representing the amount of the wall voltage generated and is dependent upon the frequency, the pulse width and the rise time of the sustain voltage in addition to components of the cell). The waveform of the sustain voltage can be made a desired one other than that depicted in FIG. 8.

Under the first condition, when the voltage pen 14, which is being supplied with a sinusoidal control voltage V having a frequency of ZOKHz and a peak-topeak voltage of 200V from the control voltage source 13, is placed on the gas discharge display device at a desired position, a pulse discharge is caused in the cell of that position, by which a discharge spot is continuously produced in the same manner as in the case of addressing with the X- and Y-direction electrodes as described above, even if the voltage pen 14 is removed from the gas discharge display device 10.

In the writing operation described above, when the voltage pen 14 is put on the gas discharge display device 10, a weak discharge is caused only by the voltage at the tip of the pen and electrons and ions produced by the weak voltage become a discharge current to cause a decrease in the firing voltage at the addressed position and, as a result of this, a main discharge is caused by the sustain voltage V at the addressed position. Accordingly, at the time of the writing operation, the sustain voltage V is preferred to be set at a value as close to the firing voltage V as possible, that is, at a maximum sustain voltage V However, if the voltage impressed to the voltage pen 14 is high and the composite voltage impressed to the discharge cell becomes higher than the firing voltage V the sustain voltage V may also be selected at an ordinary value.

FIG. 9 illustrates a waveform which is produced when the writing operation is achieved by a voltage comprising the voltage V of the voltage pen 14 is superimposed upon the sustain voltage V At a time when the superimposed voltage exceeds the firing voltage V a discharge spot is produced and the writing operation is carried out.

Next, a description will be made in connection with the erasing operation by the voltage pen 14. The changeover switch S is turned to position b and the voltage or frequency of the sustain voltage derived from the sustain voltage generator circuit 11 is lowered in the converter circuit 12, whose output is impressed upon the X- and Y-direction electrodes of the gas discharge display device 10. This condition is a second condition with a small memory factor. The sustain voltage for providing the second condition is selected at a value close to the minimum sustain voltage v or its frequency is lowered. The limit of the frequency is different according to the characteristic of the gqs discharge display device 10, and hence is difficult to express quantitatively but qualitatively it is the lowest frequency at which continuous generation of the discharge spot is possible. The memory factor represents the quantity of wall charge and exhibits a mountainshaped characteristic. At frequencies higher than an optimum frequency, polarity inversion of the sustain voltage takes places at a speed higher than the migration speed of charged particles to cause a decrease in the wall voltage; while at frequencies lower than the optimum frequency, the discharge intervals become longer and wall charge is neutralized and extinguished until the subsequent discharge.

FIG. 10 illustrates the internal construction of the voltage converter circuit, in which terminals 121 and 122 are connected to those 117 and 118 of the sustain voltage generator circuit 11 respectively, and terminals 123 and 124 are connected to those 152 and 162 of the address circuits 15 and 16 respectivelynUpon conduction of transistors 05 and Q6, the minimum sustain voltage V is impressed to the X- and Y-direction electrodes of the gas discharge display device 10. Namely, a minimum voltage for maintaining the discharge spot being generated is impressed to the electrodes of the gas discharge display device 10 and a voltage is applied by the voltage pen 14 to an addressed position. In such a case, a discharge spot is produced but a sufficient wall voltage V is not provided and, after the next half cycle, the potential difference between the wall voltage V and the minimum sustain voltage V does not exceed the firing voltage V and the discharge spot becomes extinguished. Namely, the display can be erased. The waveform in this case is depicted in FIG. 11. Also in the case where the potential difference between the voltage impressed by the voltage pen l4 and the minimum sustain voltage V does not exceed the firing voltage V the wall voltage V is converged to a lower level and erasing is achieved.

Where the wall voltage V is at a certain level, for example, as shown in FIG. 12, impression of the maximum sustain voltage V causes the wall voltage V to approach a certain higher level, so that a discharge spot can be continuously produced by its weak discharge. However, impression of the minimum sustain voltage V causes the wall voltage V to be converged close to zero level and the discharge spot becomes extinguished. Namely, where the maximum sustain voltage V is being impressed, writing can be effected even by a slight discharge due to the voltage pen 14, but in the case where the minimum sustain voltage V is being impressed, when the wall voltage V is temporarily neutralized and lowered by a slight discharge due to the voltage pen 14, the wall voltage V is immediately converged to zero level and, as a result of this, the discharge spot becomes extinguished. Illustratively, the maximum sustain voltage V is about 150V and the minimum sustain voltage V is about 140V, and an increase in the difference there between further ensures writing and erasing operations.

The minimum sustain voltage V can also be produced by a suitable control in the sustain voltage generator circuit 11 and not through the provision of the voltage converter 12 and since this requires merely control of the peak value, the circuit construction therefor is relatively simple.

In the foregoing example, the sustain voltage is made minimum at the time of the erasing operation but the erasing operation can also be achieved by lowering its frequency. In such a case, the converter circuit is a frequency converter circuit, whose internal construction is depicted in FIG. 10B. Terminals 121a, 122a, 123a and 124a are connected in the same manner as those 121 to 124 in FIG. 10A. Reference numerals 125 and 126 indicate dividers, which divide the frequency of the sustain voltage output derived from the sustain voltage generator circuit 11. By the frequency divided output, transistors Q7 and Q8 are controlled to impress a sustain voltage of low frequency to the X- and Y-direction electrodes of the gas discharge display device 10.

In the second condition with such a sustain voltage of relatively low frequency being applied to the electrodes, when the voltage pen 14 is placed at a desired discharge spot position, a weak discharge is caused only by the voltage at the tip of the pen 14 as is the case with the writing operation and charged particles produced by this weak discharge act to neutralize the wall voltage produced by the main discharge. Namely, under this second condition, the memory factor of the main discharge maintained by the sustain voltage is extremely small, so that, by somewhat forcibly neturalizing the wall voltage with the discharge caused by the voltage of the tip of the pen 14, the main discharge is no longer caused and the discharge spot is erased. Where the. voltage pen 14 is put on a portion where no discharge spot exists, a weak discharge might be seen while the voltage pen is held at that portion but no wall charge is produced due to the above neutralizing phenomenon, so that the discharge is not maintained after the voltage pen is removed. To ensure this operation, it is effective to reduce the amplitude of the sustain voltage close to the minimum sustain voltage in addition to the frequency conversion.

In our experiment in which use was made of a display panel having sealed therein an ionizable gas composed of Ne with a small amount of N under a pressure of 500 Torr. and having a gap spacing of 200p, the thickness of the base plate on the address side being 700;, and write-in address was achieved with the sustain voltage V and the control voltage V of the aforementioned values and, positive writing operation was confirmed. Further, when erasing address was carried out with the sustain voltage V having a frequency of lOKHz, only an addressed discharge spot could be positively erased.

In this example, the control voltage fed to the voltage pen 14 causes a weak discharge in the cell and this discharge is utilized to fire and erase the main discharge but in accordance with other examples of this invention external addressing is possible with a control voltage of lower frequency.

Namely, as is the case with the writing operation described above, when the control voltage V of relatively low frequency is impressed to the display panel from the voltage pen while the sustain voltage V of relatively high frequency is applied to the display panel, the both voltages are combined together and such a biased sustain voltage as shown in FIG. 9 is applied to the portion addressed by the voltage pen 14. The sustain voltage thus biased by the control voltage V is substantially equal to a write-in voltage in a slow address method published at an earlier stage of development of this kind of display panel, so that the addressed portion starts pulse discharge when this sustain voltage exceeds the firing voltage.

ln the erasing, since the frequency of the sustain voltage V is lowered, the composite voltage with the control voltage V has such a complicated waveform as depicted in FIG. 13, and fine pulses E produced at random in the portion contributing to discharge, serve as erasing pulses. It is known that where a pulse of a pulse width less than a certain value (usually 3uS) is applied to the discharging portion, generation of the wall voltage can be stopped. Considering that the frequency of the control voltage is 10 to ZOKHz, to assure that such erasing pulses as above mentioned are produced while the voltage pen 14 is slowly moved by hand, it further is proposed to positively swing or vary one or both of the frequencies of the sustain voltage and the control voltage so as to provide for enhanced probability of generation of the composite voltage acting as the erasing pulse and hence insure the erasing operation. This can easily be accomplished, for example, by the combination of a simple charge and discharge circuit with the device of this invention.

The methods of utilizing the weak discharge and the composite voltage are both the same in that the frequency of the sustain voltage is changed. In the present invention, it is considered that the two phenomena are added to each other in practice to achieve positive writing and erasing operations.

It is preferred that the gas discharge panel for use in this invention is such that the one base plate serving as an outer wall on the address side is as thin as possible to ensure that the voltage applied to the voltage enters the cell as effectively as possible. For example, it is considered to form lattice-like or dot-like grooves in the surface on the address side, minimize the voltage distributed to the base plate and use the grooves as a guide for the tip of the voltage pen. The thickness of this base plate is related to the pitch of the X- and Y-direction electrodes and where the thickness of the base plate becomes about three times the. pitch of the electrodes, one-point address is difficult.

The shape of the tip of the voltage pen 14 is preferred to be bent rather than needle-shaped for the purpose of avoiding misaddress. In order to center an electric field on'the addressed portion, it would be more effective to provide a shield cover in the neighborhood of the tip of the pen. Further, since a high voltage is applied to the voltage pen, it is desired to cover its surface with an insulating film so as to avoid danger of an electric shock. Needless to say, the changeover switch S for changing over the aforementioned frequency or voltage may be mounted on the voltage pen 14. Further, it is also possible to change over the frequency and the voltage simultaneously to provide for ensured operation.

As has been described in the foregoing, the present invention achieves writing and erasing by changing over the sustain voltage and/or its frequency at the time of the writing and erasing operations by the voltage pen 14. In the case of changing over the sustain voltage, it is sufficient only to change its peak value, while in the case of changing over its frequency, it is sufficient only to divide it, so that the circuit construction is simple and writing and erasing can be achieved positively. Accordingly, the gas discharge display device can be used as a display device of the type conventional with electronic computers and further can be adapted for a wide range of new uses.

The present invention is not limited specifically to the foregoing examples and many modifications and variations may be effected without departing from the scope of the spirits defined in the appended claims.

We claim:

l. A method of controlling a gas discharge display apparatus having an ionizable gas sealed therein and first and second sets of electrodes spaced from each other and disposed to define intersections establishing discrete display points, said method comprising the operations of: r

a. applying a sustaining voltage between the first and second sets of electrodes thereby to establish the sustaining voltage at each display point of the gas discharge display apparatus, the sustaining voltage being selected as to its frequency and amplitude values, in relation to the characteristics of the said display appartus, to be sufficient to maintain an established discharge at each said display point and insufficient for initiating a discharge thereat,

b. impressing an AC voltage to an addressing instrument and disposing the instrument on the gas discharge display apparatus at a display point to be addressed while continuing to apply the sustaining voltage between the first and second sets of electrodes, said AC voltage being selected as to its amplitude and frequency values in relation to the corresponding said values of said sustaining voltage thereby to initiate a discharge at the addressed display point which is sustained thereafter by said sustaining voltage to achieve writing; and

. altering at least one of the said frequency and amplitude values of the sustaining voltage from the value thereof applied to the gas discharge display apparatus during writing and impressing the same said AC voltage to said addressing instrument, to terminate thereby the discharge at a display point where the addressing instrument is disposed, to achieve erasing.

2. A method of controlling a gas discharge display apparatus in accordance with claim 1, wherein the amplitude value of the sustaining voltage at the time of writing is increased to a maximum sustaining value, said maximum sustaining amplitude value being less than that of the firing voltage of the display apparatus.

3. A method of controlling a gas discharge display apparatus in accordance with claim 1, wherein the amplitude value of the sustaining voltage at the time of erasing is altered by being decreased to a minimum sustaining voltage amplitude value.

4. A method of controlling a gas discharge display apparatus as claimed in claim 1, wherein the frequency value of the sustaining voltage is altered by being reduced at the time of erasure to a minimum frequency value required to sustain a discharge.

5. A method of controlling a gas discharge display apparatus as claimed in claim 1, wherein the frequency of at least one of the AC voltage impressed upon the addressing instrument and the sustaining voltage is varied during erasing.

6. Apparatus for controlling the writing and erasing of information upon a gas discharged display device 4 comprising an envelope for sealing an ionizable gas therein, and first and second sets of electrodes spaced from each other and defining intersecting points as to each other, establishing thereby discrete points where information may be written and erased, said apparatus comprising:

a. an addressing instrument disposable at a selected one of the discrete points of said gas discharge display device;

b. source means for applying an AC control voltage of selected amplitude and frequency values to said addressing instrument whereby a corresponding AC voltage is impressed upon the selected discrete point of said gas discharge display device;

c. sustaining means for impressing a sustaining voltage of selected amplitude and frequency values between the electrodes of the first and second sets whereby the sustaining voltage is applied to each discrete display point of said gas discharge display device; and

d. erasing means for varying at least one of said amplitude and frequency values of the sustaining voltage from the selected value to terminate the discharge at the discrete display point where the addressing instrument is disposed, said addressing instrument having an AC control voltage applied thereto during erasing which has at least the same said selected amplitude value as the said AC control voltage applied thereto during writing.

7. Apparatus as claimed in claim 6, wherein there is further provided first and second addressing means respectively coupled to said first and second sets of electrodes for selectively applying an addressing signal to a selected electrode of each of said first and second sets to establish a discharge at the corresponding intersection of the said selected electrodes thereby to achieve writing on said discharge display apparatus.

8. Apparatus as claimed in claim 6, wherein said gas discharge display device has a maximum amplitude value of its sustaining voltage which is slightly less than its firing voltage and a minimum sustaining voltage amplitude value, said sustaining means selecting the sustaining voltage amplitude value to be essentially equal to the said maximum sustaining voltage amplitude value during writing.

9. Apparatus as claimed in claim 8, wherein said erasing means reduces the amplitude value of the sustaining voltage output of said sustaining means to essentially the said minimum sustaining voltage amplitude value, during erasing.

10. Apparatus for controlling the writing and erasing of information upon a gas discharge display device comprising an envelope for sealing an ionizable gas therein, first and second sets of electrodes spaced from each other by the ionizable gas and intersecting each other to define discrete points where information may be written and erased, said apparatus comprising:

a. an addressing instrument disposable at a selected one of the discrete points of said gas discharge display device;

b. source means for applying an AC control voltage to saidaddressing instrument whereby a corresponding AC voltage is impressed upon the selected discrete point of said gas discharge display device;

c. sustaining means for impressing a sustaining voltage of a selected level between the electrodes of the first and second sets whereby the sustaining voltage is impressed at each discrete point of said gas discharge display device; and

d. erasing means for varying the sustaining voltage from the selected level to terminate the discharge across the discrete point where the addressing instrument is disposed, said erasing means including means for dividing the frequency of the sustaining voltage to be applied to the electrodes of said gas discharge display device.

11. Apparatus for controlling as claimed in claim 6, wherein said erasing means varies the amplitude of the sustaining voltage.

12. Apparatus for controlling as claimed in claim 6, wherein said erasing means varies the frequency of the sustaining voltage.

13. A method of controlling a gas discharge display apparatus as claimed in claim 1, wherein the frequency of the sustaining voltage is varied at the time of erasure.

14. A method as recited in claim 1, wherein:

the sustaining voltage comprises a train of bipolar pulses applied in alternating succession to said first and second sets of electrodes, and

the AC control voltage is sinusoidal, one half period thereof exceeding the interval of successive pulses of the bipolar pulse train.

15. A method of controlling a gas discharge display apparatus having an ionizable gas sealed therein and first and second sets of electrodes spaced from each other and disposed to define intersections establishing discrete display points, said method comprising the operations of:

applying a sustaining voltage between the first and second sets of electrodes thereby to establish the sustaining voltage at each display point of the gas discharge display apparatus; impressing an AC voltage to an addressing instrument and disposing the instrument on the gas discharge display apparatus at a display point to be addressed while continuing to apply the sustaining voltage between the first and second sets of electrodestat the addressed display point which is sustained thereafter by said sustaining voltage to achieve writing; and

reducing the amplitude of the sustaining voltage from the level thereof applied to the gas discharge display apparatus during writing to a minimum sustaining amplitude level, and supplying an AC voltage to said addressing instrument, to terminate thereby the discharge at a display point where the addressing instrument is disposed, to achieve erasmg.

16. A method as recited in claim 15 wherein:

the sustaining voltage comprises a train of bipolar pulses applied in alternating succession to said first and second sets of electrodes, and

the AC control voltage is sinusoidal, one half period thereof exceeding the interval of successive pulses of the bipolar pulse train.

17. A method of controlling a gas discharge display apparatus having an ionizable gas sealed therein and first and second sets of electrodes spaced from each other and disposedto define intersections establishing discrete display points, said method comprising the operations of:

applying a sustaining voltage between the first and second sets of electrodes thereby to establish the sustaining voltage at each display point of the gas discharge display apparatus, impressing an AC voltage to an addressing instrument and disposing the instrument on the gas discharge display apparatus at a display point to be addressed while continuing to apply the sustaining voltage between the first and second sets of electrodes thereby to initiate a discharge at the addressed display point which is sustained thereafter by said sustaining voltage to achieve writing; and

reducing the frequency of the sustaining voltage from the level thereof applied to the gas discharge display apparatus during writing to a minimum frequency level sufficient for sustaining a discharge, and supplying an AC voltage to said addressing instrument, to terminate thereby the discharge at a display point where the addressing instrument is disposed, to achieve erasing.

18. A method as recited in claim 17, wherein:

the sustaining voltage comprises a train of bipolar pulses applied in alternating succession to said first and second sets of electrodes, and

the AC control voltage'is sinusoidal, one half period thereof exceeding the interval of successive pulses of the bipolar pulse train:

19. A method of controlling a gas discharge display apparatus as claimed in claim 17, wherein the frequency of at least one of the AC voltage impressed upon the writing instrument and the sustaining voltage is varied during erasing.

20. A method of controlling a gas discharge display device having an ionizable gas therein and first and second sets of electrodes disposed in spaced planes and intersecting relationship, defining therebetween a discharge region at each such intersection and thereby a corresponding, discrete display position, comprising the operations of applying a sustaining voltage to said sets of electrodes of an amplitude value selected to be sufficient to maintain a wall charge in said device in each display region at which a discharge is occuring,

writing in said device at a selected display position by positioning an addressing instrument at the selected display position and applying an AC control voltage to the instrument while continuing to apply the sustaining voltage to said sets of electrodes,

erasing said device at a selected display position by positioning the instrument at the selected position, applying an AC control voltage thereto, and altering at least one of the frequency and amplitude values of the sustaining voltage,

said sustaining voltage at all times having amplitude and frequency values sufficient to produce a wall voltage for maintaining an already existing discharge, and the values thereof being selected with respect to those of the AC control voltage to produce, in the write operation, a composite voltage of sufficient amplitude and appropriate frequency for initiating a discharge and producing a resultant wall voltage thereafter maintainable by said sus taining voltage alone, for sustaining the discharge, and to result, in the erase operation, in a composite voltage which effects discharging of an existing wall voltage but which is not sufficient to maintain the wall voltage, thereby terminating the discharge 21. Apparatus for controlling a gas discharge display device having an ionizable gas therein and first and second sets of electrodes disposed in spaced planes and intersecting relationship, defining therebetween a discharge display region at each such intersection and thereby a corresponding, discrete display position, comprising means for applying a sustaining voltage to said sets of electrodes of an amplitude value selected to be sufficient to maintain a wall charge in said device in each display region at which a discharge is occurring,

an addressing instrument for positioning at a selected display position,

means for applying an AC control voltage to the instrument,

said instrument being effective to write in said display device at a selected display position by positioning the instrument, with the AC control voltage applied thereto, at the selected position while the sustaining voltage is applied to said sets of electrodes,

means fr erasing said device at a selected display position at which the instrument, having the AC control voltage applied thereto, is positioned, said tiating a discharge and producing a resultant wall voltage thereafter maintainable by said sustaining voltage alone, for sustaining the discharge, and to result, in the erase operation, in a composite voltage which effects discharging of an existing wall voltage but which is not sufficient to maintain the wall voltage, thereby terminating the discharge. 

1. A method of controlling a gas discharge display apparatus having an ionizable gas sealed therein and first and second sets of electrodes spaced from each other and disposed to define intersections establishing discrete display points, said method comprising the operations of: a. applying a sustaining voltage between the first and second sets of electrodes thereby to establish the sustaining voltage at each display point of the gas discharge display apparatus, the sustaining voltage being selected as to its frequency and amplitude values, in relation to the characteristics of the said display appartus, to be sufficient to maintain an established discharge at each said display point and insufficient for initiating a discharge thereat, b. impressing an AC voltage to an addressing instrument and disposing the instrument on the gas discharge display apparatus at a display point to be addressed while continuing to apply the sustaining voltage between the first and second sets of electrodes, said AC voltage being selected as to its amplitude and frequency values in relation to the corresponding said values of said sustaining voltage thereby to initiate a discharge at the addressed display point which is sustained thereafter by said sustaining voltage to achieve writing; and c. altering at least one of the said frequency and amplitude values of the sustaining voltage from the value thereof applied to the gas discharge display apparatus during writing and impressing the same said AC voltage to said addressing instrument, to terminate thereby the discharge at a display point where the addressing instrument is disposed, to achieve erasing.
 2. A method of controlling a gas discharge display apparatus in accordance with claim 1, wherein the amplitude value of the sustaining voltage at the time of writing is increased to a maximum sustaining value, said maximum sustaining amplitude value being less than that of the firing voltage of the display apparatus.
 3. A method of controlling a gas discharge display apparatus in accordance with claim 1, wherein the amplitude value of the sustaining voltage at the time of erasing is altered by being decreased to a minimum sustaining voltage amplitude value.
 4. A method of controlling a gas discharge display apparatus as claimed in claim 1, wherein the frequency value of the sustaining voltage is altered by being reduced at the time of erasure to a minimum frequency value required to sustain a discharge.
 5. A method of controlling a gas discharge display apparatus as claimed in claim 1, wherein the frequency of at least one of the AC voltage impressed upon the addressing instrument and the sustaining voltage is varied during erasing.
 6. Apparatus for controlling the writing and erasing of information upon a gas discharged display device comprising an envelope for sealing an ionizable gas therein, and first and second sets of electrodes spaced from each other and defining intersecting points as to each other, establishing thereby discrete points where information may be written and erased, said apparatus comprising: a. an addressing instrument disposable at a selected one of the discrete points of said gas discharge display device; b. source means for applying an AC control voltage of selected amplitude and frequency values to said addressing instrument whereby a corresponding AC voltage is impressed upon the selected discrete point of said gas discharge display device; c. sustaining means for impressing a sustaining voltage of selected amplitude and frequency values between the electrodes of the first and second sets whereby the sustaining voltage is applied to each discrete display point of said gas discharge display device; and d. erasing means for varying at least one of said amplitude and frequency values of the sustaining voltage from the selected value to terminate the discharge at the discrete display point where the addressing instrument is disposed, said addressing instrument having an AC control voltage applied thereto during erasing which has at least the same said selected amplitude value as the said AC control voltage applied thereto during writing.
 7. Apparatus as claimed in claim 6, wherein there is further provided first and second addressing means respectively coupled to said first and second sets of electrodes for selectively applying an addressing signal to a selected electrode of each of said first and second sets to establish a discharge at the corresponding intersection of the said selected electrodes thereby to achieve writing on said discharge display apparatus.
 8. Apparatus as claimed in claim 6, wherein said gas discharge display device has a maximum amplitude value of its sustaining voltage which is slightly less than its firing voltage and a minimum sustaining voltage amplitude value, said sustaining means selecting the sustaining voltage amplitude value to be essentially equal to the said maximum sustaining voltage amplitude value during writing.
 9. Apparatus as claimed in claim 8, wherein said erasing means reduces the amplitude value of the sustaining voltage output of said sustaining means to essentially the said minimum sustaining voltage amplitude value, during erasing.
 10. Apparatus for controlling the writing and erasing of information upon a gas discharge display device comprising an envelope for sealing an ionizable gas therein, first and second sets of electrodes spaced from each other by the ionizable gas and intersecting each other to define discrete points where information may be written and erased, said apparatus comprising: a. an addressing instrument disposable at a selected one of the discrete points of said gas discharge display device; b. source means for applying an AC control voltage to said addressing instrument whereby a corresponding AC voltage is impressed upon the selected discrete point of said gas discharge display device; c. sustaining means for impressing a sustaining voltage of a selected level between the electrodes of the first and second sets whereby the sustaining voltage is impressed at each discrete point of said gas discharge display device; and d. erasing means for varying the sustaining voltage from the selected level to terminate the discharge across the discrete point where the addressing instrument is disposed, said erasing means including means for dividing the frequency of the sustaining voltage to be applied to the electrodes of said gas discharge display device.
 11. Apparatus for controlling as claimed in claim 6, wherein said erasing means varies the amplitude of the sustaining voltage.
 12. Apparatus for controlling as claimed in claim 6, wherein said erasing means varies the frequency of the sustaining voltage.
 13. A method of controlling a gas discharge display apparatus as claimed in claim 1, wherein the frequency of the sustaining voltage is varied at the time of erasure.
 14. A method as recited in claim 1, wherein: the sustaining voltage comprises a train of bipolar pulses applied in alternating succession to said first and second sets of electrodes, and the AC control voltage is sinusoidal, one half period thereof exceeding the interval of successive pulses of the bipolar pulse train.
 15. A method of controlling a gas discharge display apparatus having an ionizable gas sealed therein and first and second sets of electrodes spaced from each other and disposed to define intersections establishing discrete display points, said method comprising the operations of: applying a sustaining voltage between the first and second sets of electrodes thereby to establish the sustaining voltage at each display point of the gas discharge display apparatus; impressing an AC voltage to an addressing instrument and disposing the instrument on the gas discharge display apparatus at a display point to be addressed while continuing to apply the sustaining voltage between the first and second sets of electrodes at the addressed display point which is sustained thereafter by said sustaining voltage to achieve writing; and reducing the amplitude of the sustaining voltage from the level thereof applied to the gas discharge display apparatus during writing to a minimum sustaining amplitude level, and supplying an AC voltage to said addressing instrument, to terminate thereby the discharge at a display point where the addressing instrument is disposed, to achieve erasing.
 16. A method as recited in claim 15 wherein: the sustaining voltage comprises a train of bipolar pulses applied in alternating succession to said first and second sets of electrodes, and the AC control voltage is sinusoidal, one half period thereof exceeding the interval of successive pulses of the bipolar pulse train.
 17. A method of controlling a gas discharge display apparatus having an ionizable gas sealed therein and first and second sets of electrodes spaced from each other and disposed to define intersections establishing discrete display points, said method comprising the operations of: applying a sustaining voltage between the first and second sets of electrodes thereby to establish the sustaining voltage at each display point of the gas discharge display apparatus, impressing an AC voltage to an addressing instrument and disposing the instrument on the gas discharge display apparatus at a display point to be addressed while continuing to apply the sustaining voltage between the first and second sets of electrodes thereby to initiate a discharge at the addressed display point which is sustained thereafter by said sustaining voltage to achieve writing; and reducing the frequency of the sustaining voltage from the level thereof applied to the gas discharge display apparatus during writing to a minimum frequency level sufficient for sustaining a discharge, and supplying an AC voltage to said addressing instrument, to terminate thereby the discharge at a display point where the addressing instrument is disposed, to achieve erasing.
 18. A method as recited in claim 17, wherein: the sustaining voltage comprises a train of bipolar pulses applied in alternating succession to said first and second sets of electrodes, and the AC control voltage is sinusoidal, one half period thereof exceeding the interval of successive pulses of the bipolar pulse train.
 19. A method of controlling a gas discharge display apparatus as claimed in claim 17, wherein the frequency of at least one of the AC voltage impressed upon the writing instrument and the sustaining voltage is varied during erasing.
 20. A method of controlling a gas discharge display device having an ionizable gas therein and first and second sets of electrodes disposed in spaced planes and intersecting relationship, defining therebetween a discharge region at each such intersection and thereby a corresponding, discrete display position, comprising the operations of applying a sustaining voltage to said sets of electrodes of an amplitude value selected to be sufficient to maintain a wall charge in said device in each display region at which a discharge is occuring, writing in said device at a selected display position by positioning an addressing instrument at the selected display position and applying an AC control voltage to the instrument while continuing to apply the sustaining voltage to said sets of electrodes, erasing said device at a selected display position by positioning the instrument at the selected position, applying an AC control voltage thereto, and altering at least one of the frequency and amplitude values of the sustaining voltage, said sustaining voltage at all times having amplitude and frequency values sufficient to produce a wall voltage for maintaining an already existing discharge, and the values thereof being selected with respect to those of the AC control voltage to produce, in the write operation, a composite voltage of sufficient amplitude and appropriate frequency for initiating a discharge and producing a resultant wall voltage thereafter maintainable by said sustaining voltage alone, for sustaining the discharge, and to result, in the erase operation, in a composite voltage which effects discharging of an existing wall voltage but which is not sufficient to maintain the wall voltage, thereby terminating the discharge.
 21. Apparatus for controlling a gas discharge display device having an ionizable gas therein and first and second sets of electrodes disposed in spaced planes and intersecting relationship, defining therebetween a discharge display region at each such intersection and thereby a corresponding, discrete display position, comprising means for applying a sustaining voltage to said sets of electrodes of an amplitude value selected to be sufficient to maintain a wall charge in said device in each display region at which a discharge is occurring, an addressing instrument for positioning at a selected display position, means for applying an AC control voltage to the instrument, said instrument being effective to write in said display device at a selected display position by positioning the instrument, with the AC control voltage applied thereto, at the selected position while the sustaining voltage is applied to said sets of electrodes, means fr erasing said device at a selected display position at which the instrument, having the AC control voltage applied thereto, is positioned, said erasing means altering at least one of the frequency and amplitude values of the sustain voltage, said sustain voltage at all times having amplitude and frequency values sufficient to produce a wall voltage for maintaining an already existing discharge, and the values thereof being selected with respect to those of the AC control voltage to produce, in the write operation a composite voltage of sufficient amplitude and appropriate frequency for initiating a discharge and producing a resultant wall voltage thereafter maintainable by said sustaining voltage alone, for sustaining the discharge, and to result, in the erase operation, in a composite voltage which effects discharging of an existing wall voltage but which is not sufficient to maintain the wall voltage, thereby terminating the discharge. 